1. Field of the Invention
The present invention relates to microemulsions containing alkanolammonium salts of the alkylsulfates and/or alkylpolyalkyleneglycolethersulfates and the use thereof for cosmetic and/or medicinal-dermatologic applications.
2. Description of the Prior Art
In particular, microemulsions are increasingly used for applications in which it is desirable to simultaneously employ an aqueous phase and an oil component. For a survey of microemulsion applications, see e.g. Chhabra, V., et al. in Tensid Surf. Det., 34 (1997), p. 156-168. In said publication for example the use of microemulsions in cleansers is described.
There is also an interest in emulsions for cosmetic and medicinal-dermatologic applications. Compositions which are intended for use both as body cleaners and body care preparations must fulfill different requirements, e.g. combining the cleaning properties of an aqueous surfactant formulation with the cosmetic properties of an oil component. The compositions of preparations employed both as body cleaners and body care preparations are different from conventional cleaners utilized for instance for cleaning floors, textiles, or dishes.
Skin and hair are usually cleaned with surfactants, which will effect more or less pronounced swelling and subsequent dehydration of the horn layer of the skin, thereby impairing the protective mechanism of the skin surface. Therefore, skin care components allowing regeneration of the skin are increasingly added to customary skin cleaning preparations. It is furthermore possible to add excitometabolic components to these preparations, thus improving the general condition. This is particularly true of foam bath oils, which have been commercially available lately. Besides other active ingredients, these substantially anhydrous preparations contain surfactants for cleaning the skin and a large quantity of oils for treating the skin. The disadvantage of the foam bath oils is that the major portion of the oil remains on the water surface in the bath tub, thus having only little contact with the skin and a poor regenerating effect. The oil remains largely unused in the waste water.
The facts are similar with shower oil preparations, e.g. those described in U.S. Pat. No. 5,653,988 or DE 197 12 678-A1. The formulations disclosed therein are substantially anhydrous, surfactant-containing, cosmetic or dermatologic shower oils, which contain at least 45% or 30% of one or more oil component(s). With these products, too, the major portion of the oil components is washed away unused when taking a shower bath because the oil in the products is present in excess.
Another disadvantage of foam bath oils and shower oils is the high price of the ingredients, which contain no or only little water. Therefore, many efforts have hitherto been made to reduce the oil content, while increasing the water content, preserving the foaming power, and improving the price/performance ratio.
U.S. Pat. No. 4,371,548 discloses foaming and surfactant-containing bath and shower preparations having an oil content of from 20 to 60% and, optionally, a water content of max. 15%. These preparations have disadvantages and furthermore still have a poor price/performance ratio because the water content is kept low in order to preserve the desirable properties (good cleaning of the skin, good foaming power, intense skin care effect).
The type of oil component, the amount used in a formulation, the percentage of the aqueous phase and its composition are frequently predetermined by the requirements of the individual fields of application. While the expert knows how to select an appropriate surfactant from among the large variety of commercially available products for making a macroemulsion, the manufacture of a microemulsion presents considerable problems because the phase areas of an oil-water-surfactant blend, wherein a macroemulsion is formed, are considerably larger than those in which microemulsions are formed.
Numerous attempts were made in the past to manufacture preparations, which are both body cleaners and body care products. The terms “body cleaner” and “body care product” used herein shall mean any product employed for cleaning and treating hair and/or skin during showering, washing, or bathing.
When employing the compositions of the present invention for cosmetic and medicinal-dermatologic applications, it has been surprisingly discovered that the microemulsions of the invention are capable of combining the cleaning properties of an aqueous surfactant formulation and the cosmetic properties of an oil component, thereby effecting better spreading of the cosmetic oil component on the skin as a result of the fine dispersion of the oil droplets in the microemulsion.
When formulating cosmetic or medicinal-dermatologic preparations, the problem is aggravated by the fact that the surfactants employed for making the microemulsions should be non-irritant to the skin, the selection of a suitable surfactant thus being more difficult.
The microemulsions described in literature mostly comprise nonionic surfactants, e.g. alcohol ethoxylates. When using these surfactants in preparations intended for application to human skin, they have the disadvantage to cause intolerably high defatting of the skin. Anionic surfactants often require co-emulsifiers to make microemulsions.
Microemulsions containing alkylpolyalkyleneglycolethersulfates or alkylsulfates are known per se. DE 35 34 733 A1 discloses foaming surfactant preparations with clear-solubilized, water-insoluble oil components, which are usually termed microemulsions. In said publication it is explicitly pointed out that lower alcohols or alkylglycols having C1- to C4-alkyl groups need not be employed. EP 0 638 634 A2 discloses surfactant microemulsions as all-purpose cleaners, which inevitably contain surfactants of the sulfonate type. However, such surfactants are inappropriate for cosmetic applications.